The present invention relates generally to wheel spin control of a motor vehicle and, more particularly, to a system and method for controlling wheel spin of a vehicle by controlling the operation of the clutches in a multiple clutch transmission.
Surface conditions of roadways are prone to vary unexpectedly. When a vehicle encounters a slippery surface, engine torque applied to a driven wheel may cause the wheel to abruptly accelerate or spin and result in a temporary loss of vehicle control. Faced with such a situation, usually an operator of the vehicle will quickly reduce wheel speed to thereby stop the spin of the driven wheel and maintain control of the vehicle. Unfortunately, operators lack the ability to control wheel spin and oftentimes lose control of the vehicle.
Various techniques have been proposed to assist a vehicle operator by preventing wheel spin on slippery surfaces. For example, U.S. Pat. No. 4,768,608 discloses a system for controlling wheel slip of a vehicle by reducing the output torque of the engine when wheel slip is detected. Wheel slip of the vehicle is detected by measuring the difference in speed between a driven wheel and a non-driven wheel and comparing this calculated difference to a preset value. The engine intake manifold pressure of the vehicle is also monitored and a composite control signal is produced from the sum of the wheel slip and manifold pressure signals. In response to the composite control signal, the engine throttle is reduced, thereby reducing the output torque of the engine. A problem with this approach is that the transient response time of the above control system is limited by the time delay associated with reducing the engine torque and transmitting engine torque through the drive train and wheels.
In commonly assigned U.S. Pat. No. 5,020,622, wheel spin is reduced by controlling the slip rate of an electronically controlled, hydraulically operated clutch. Wheel spin is detected by comparing the speed of a driven wheel to the speed of a non-driven wheel. In response to feedback signals indicative of detected wheel spin and hydraulic pressure being applied to a clutch driving the driven wheel, the clutch hydraulic pressure is regulated to increase the clutch slip rate. The increased clutch slip rate reduces the torque transferred from the engine to the driven wheel, thus reducing wheel spin. Additionally, the engine speed is adjusted in response to the wheel spin feedback signal to prevent over-revving of the engine and maintaining a positive torque on the driven wheel while the clutch is being slipped. Since the clutch being slipped is transferring torque from the engine to the driven wheel, the slip rate of the clutch must be precisely controlled to ensure that the torque path from the engine to the driven wheel is not interrupted. Unfortunately, relatively complex circuitry is required to precisely control the slip rate of the clutch.
Accordingly, there is a need for an efficient and less complex vehicle wheel spin control system which maintains the drive train torque path while reducing the wheel spin of the vehicle.